Semicoductor chip and method for production thereof

ABSTRACT

For producing semiconductor chips by thin-film technology, an active layer ( 2 ) that has been grown on a substrate, with contact layers on the back side that have a base layer ( 3 ), is reinforced by a reinforcement layer ( 4 ). Next, an auxiliary carrier layer ( 5 ) is applied, which makes the further processing of the active layer ( 2 ) possible. The reinforcement layer ( 4 ) and the auxiliary carrier layer ( 5 ) replace the mechanical carriers used in conventional methods.

[0001] The invention relates to a semiconductor chip, with an active layer that has a photon-emitting zone, with contact points embodied on both sides of the active layer.

[0002] The invention also relates to a method for producing a semiconductor chip by thin-film technology, having the following method steps:

[0003] embodying an active layer, which has a photon-emitting zone, on a substrate;

[0004] embodying contact points on the active layer; and

[0005] removing the substrate.

[0006] Such semiconductor chips are known from European Patent Disclosure EP 0 905 797 A2, for instance. The active layer of these semiconductor chips is typically grown on a substrate. The substrate will in general absorb some of the photons emitted by the active layer. To increase the light yield, it is therefore known to separate the active layer from the substrate and apply it to a carrier body that is separated from the active layer by a reflective layer. Securing it to a carrier body is necessary in order to assure the requisite mechanical strength in the subsequent process steps.

[0007] One disadvantage of the known semiconductor chips is that transferring the active layer from the substrate onto the carrier body is difficult to handle. In particular, the bond between the carrier body and the active layer can in general be accomplished only by employing high mechanical pressure or an elevated temperature. Both of these can be harmful to the active layer.

[0008] With this prior art as the point of departure, it is the object of the invention to create a semiconductor chip which can be produced in a simple way by thin-film technology.

[0009] It is also the object of the invention to create a corresponding method suitable for producing the semiconductor chip.

[0010] These objects are attained by a semiconductor chip having the characteristics of claim 1 and a method having the characteristics of claim 4.

[0011] The active layer is stiffened by means of the contact layer on the back, whose thickness is at least equal to the thickness of the active layer. It is therefore unnecessary, for the sake of further processing of the active layer, to apply it to a carrier body. Moreover, contact layers of great thickness can be produced in the conventional way with the usual materials. It is therefore unnecessary for new methods to be developed in order to make contact layers that are thick enough. Overall, the invention therefore makes substantially simplified production of semiconductor chips by thin-film technology possible.

[0012] In a preferred embodiment of the method, after the galvanic application of a reinforcement layer to the contact layer, a surface-covering galvanic auxiliary carrier layer is deposited on the active layer.

[0013] By means of this kind of auxiliary carrier layer, the active layer can be developed further into a solid, rigid body that is equivalent in its mechanical properties to a wafer.

[0014] In a further preferred feature of the method, the auxiliary carrier layer is made of a material that can be removed selectively relative to the reinforcement layer.

[0015] This choice of material makes it possible for the semiconductor chips, after their processing, to be separated into individual semiconductor chips without using sawing methods. Hence there is no waste of material, and there is no need to design the semiconductor chips in such a way as to take the imprecisions of sawing into account.

[0016] Further advantageous features of the invention are the subject of the dependent claims.

[0017] The invention will be described in detail below in conjunction with the accompanying drawing. Shown are:

[0018]FIG. 1, a cross section through a layer sequence, with a substrate and an active layer applied over it that is provided with contact points on the back side;

[0019]FIG. 2, the layer sequence of FIG. 1, whose contact points on the back side have been reinforced with a reinforcement layer;

[0020]FIG. 3, the layer sequence of FIG. 2, provided with an auxiliary carrier layer;

[0021]FIG. 4, the layer sequence of FIG. 3, after the substrate has been removed;

[0022]FIG. 5, a cross section through the layer sequence of FIG. 4, provided with contact points on the front side, after the separation into individual chips;

[0023]FIG. 6, the layer sequence of FIG. 5, applied to a film; and

[0024]FIG. 7, a cross section through the separated semiconductor chips, resting on the film, after the removal of the auxiliary carrier layer.

[0025] In FIG. 1, a cross section is shown through a layer sequence that has a substrate 1. An active layer 2 is grown on the substrate 1 and includes a photon-emitting active zone.

[0026] The thickness of the active layer 2 is typically between 5 and 15 μm.

[0027] Contact layers are embodied on the back side of the active layer 2, which in the case shown have among other things a base layer 3. By way of the contact layers, current can be fed into the active layer 2.

[0028] In a further method step, shown in FIG. 2, a reinforcement layer 4 is applied galvanically to the base layers 3. The reinforcement layer 4 is made from gold, for instance, and has a thickness of 20 to 30 μm.

[0029] Next, a surface-covering auxiliary carrier layer 5 is applied to the reinforcement layer 4 and the active layer 2. The application of the auxiliary carrier layer 5 is, for instance, likewise effected galvanically.

[0030] Next, the substrate 1 is separated from the active layer 2. This creates the cross section shown in FIG. 4. The thickness of the auxiliary carrier layer 5 is dimensioned such that the layer sequence shown in FIG. 4 offers adequate mechanical strength for the ensuing process steps. The material for the auxiliary carrier layer 5 is moreover selected such that the auxiliary carrier layer 5 can be removed selectively relative to the reinforcement layer 4. For instance, the auxiliary carrier layer 5 can be made from nickel or silver, while the reinforcement layer 4 is made from gold. In that case, the auxiliary carrier layer 5 can be removed selectively relative to the reinforcement layer 4 by means of etching with nitric acid.

[0031] In a further method step, contact layers 6 are embodied on the front side of the active layer 2. The active layer 2 is then severed by an etching process. This creates individual semiconductor chips 7. The etching process is conducted such that the active layer 2 of the semiconductor chips 7 is congruent with the contact layers on the back side that are formed by the base layer 3 and the reinforcement layer 4.

[0032] To make the semiconductor chips 7 easier to handle, the semiconductor chips 7 are laminated to a film 8 on their front side. The result is the cross section through the layer sequence as shown in FIG. 6.

[0033] Finally, the auxiliary carrier layer 5 is removed selectively from the base layers 3 and reinforcement layers 4. The result is individual semiconductor chips 7 that have been applied to the film 8.

[0034] The method described offers a number of advantages.

[0035] In the method described, the mechanical carrier body used in conventional thin-film processes is replaced by the reinforcement layer 4. The reinforcement layer 4 lends the semiconductor chip 7 adequate mechanical strength, which makes it possible for the semiconductor chips 7 to be handled until they are mounted on a printed circuit board.

[0036] Once the substrate 1 has been removed, the auxiliary carrier layer 5 offers an adequate replacement for a mechanical carrier for performing the wafer processing step required to produce the semiconductor chips 7. It is therefore possible to dispense with a further mechanical carrier entirely.

[0037] The semiconductor chips 7 moreover have only the components that are indispensable for function: the active layer 2, the contact layers on the back side, formed by the base layer 3 and the reinforcement layer 4, and the contact layers 6 on the front side. The structural size of the semiconductor chips 7 can therefore also be reduced without further difficulties.

[0038] For applying the reinforcement layer 4 and auxiliary carrier layer 5, galvanic processes can be employed. These are economical standard methods. Moreover, galvanic layers can also be applied over a large area without problems, for instance without the risk that air will become trapped, a risk that is associated with the bonding of large surfaces.

[0039] It is also advantageous that the separation of the semiconductor chips 7 into individual chips is accomplished by etching processes. There is accordingly no need to use sawing methods. As a result, the utilization of the active layer 2 can be increased from 70% to approximately 90%, since on the one hand, sawing tolerances need not be taken into account in the dimensions of the semiconductor chips, and on the other, the material waste of approximately 50 μm per semiconductor chip 7 is eliminated.

[0040] The method presented is especially well suited to producing semiconductor chips for light-emitting diodes of high luminance. 

1. A semiconductor chip, with an active layer (2) that has a photon-emitting zone, onto both sides of which layer contact points are embodied, characterized in that one of the contact points is embodied as a contact layer (3, 4), whose thickness is at least equal to the thickness of the active layer (2).
 2. The semiconductor chip of claim 1, characterized in that the contact layer (3, 4) has at least twice the thickness of the active layer (2).
 3. The semiconductor chip of claim 1 or 2, characterized in that the contact layer (3, 4) is made of metal.
 4. A method for producing a semiconductor chip by thin-film technology, having the following method steps: embodying an active layer (2), which has a photon-emitting zone, on a substrate (1); embodying contact points on the active layer (2); and removing the substrate (1), characterized in that one of the contact points is embodied as a contact layer (3, 4), whose thickness is greater than the thickness of the active layer (2).
 5. The method of claim 4, characterized in that for producing the contact layer galvanically, a reinforcement layer (4) is applied to a base layer (3) applied to the active layer.
 6. The method of claim 5, characterized in that the contact layer (3, 4) has at least the thickness of the active layer (2).
 7. The method of claim 5, characterized in that the contact layer (3, 4) has at least twice the thickness of the active layer (2).
 8. The method of one of claims 5-7, characterized in that an auxiliary carrier layer (5) is applied galvanically to the reinforcement layer (4), covering the full surface.
 9. The method of claim 8, characterized in that after the application of the galvanic auxiliary carrier layer (5), the substrate (1) is removed, and contact layers (6) on the front side are embodied on the side of the active layer (2) opposite the galvanic auxiliary carrier layer (5).
 10. The method of claim 8 or 9, characterized in that the active layer (2) is separated into many semiconductor chips (7).
 11. The method of claim 10, characterized in that the semiconductor chips (7) are applied on the front side to a film (8).
 12. The method of claim 10 or 11, characterized in that in a further method step, the auxiliary carrier layer (5) is removed. 